Maximum Power Point Tracking (MPPT) is necessary because variations of sun intensity or temperature throughout the day, which vary with the illumination angle, spectrum or due to shading and may significantly shift the optimal working voltage of the solar cell. Several examples of maximum power point tracking may be found in scientific literature for Silicon based solar cells.
Perturb and Observe (PERTURB AND OBSERVE) and Incremental Conductance (IncCon) are the most used MPPT methods. In PERTURB AND OBSERVE the power output is maximized by constantly perturbing voluntarily the operating voltage, unlike steady state methods such as fractional voltage or fractional current where a constant voltage or current is applied to the solar array and is based on the knowledge of the j-V characteristics of the PV array. In PERTURB AND OBSERVE, the power of the array is sampled and compared to the previous value. The duty cycle of the buck-boost converter (ton/ttot of the gated switch) is adapted according to whether the power increases or decreases.
In IncCond, the differential conductance (dI/dV) and steady-state conductance (I/V) are calculated and the control on the duty cycle of the buck-boost converter is taken accordingly. Other examples make use of fuzzy logic, neural networks. Most investigations and tunings of MPPT algorithms focus on improving the steady-state performance, the transient response and the cost of implementation.
The presence of hysteresis between the backward voltage sweep and forward voltage sweep in perovskite cells has been extensively reported and its origin is still under debate. In such situations, the algorithm needs to deal with a non-symmetrical j-V relationship. If the hysteresis cannot be avoided, the MPPT algorithms must be adapted consequently.
In light of the above deficiencies of the background art, specifically with respect to the MPPT technology and methods, and the presence of a non-symmetricla j-V relationships, substantially improved and more sophisticated methods and devices are desired, to address these problems.